This invention generally relates to electronic systems and in particular it relates to multiple mode switching regulators.
A switching regulator provides a regulated output voltage to a load from an unregulated input voltage. A typical switching regulator has at least two switches that switch ON and OFF out of phase with each other to supply current to a load. Three types of switching regulators include: buck mode switching regulators, which regulate an output voltage that is lower than the input voltage; boost mode regulators, which regulate an output voltage that is higher than the input voltage; and buck-boost mode switching regulators, which regulate an output voltage that is higher, lower, or the same as the input voltage. These three modes can be combined to form a multiple mode switching regulator.
A typical multiple mode switching regulator includes an inductor with a first end coupled to both a first high side switch a first low side switch, and a second end coupled to both a second high side switch and a second low side switch. The first high side switch and first low side switch are on the input side. The second high side switch and second low side switch are on the output side. In buck mode, the first high side switch and first low side switch are switched ON and OFF out of phase with each other. In boost mode, the second high side switch and second low side switch are switched ON and OFF out of phase with each other. In buck-boost mode, the first high side switch and the second low side switch are switched ON and OFF in phase with each other, and the second high side switch and the first low side switch are switched ON and OFF in phase with each other, but out of phase with the first high side switch and second low side switch.
Prior art solutions typically do not work in all three modes of operation without external reconfiguration of the device. Typically, a device is configured to work in only one mode with a reduced input range, and thus does not require this type of solution.
One prior art solution adds another small boost regulator with an external inductor to be able to supply the required power. However, this adds an expensive external inductor, more circuitry, and possibly extra pins.
A multiple mode switching regulator with a bootstrap technique includes an inductor; a high side input switch coupled to a first end of the inductor; a low side input switch coupled to the first end of the inductor; a high side driver coupled to a control node of the high side input switch; a low side driver coupled to a control node of the low side input switch; a high side output switch coupled to a second end of the inductor; a low side output switch coupled to the second end of the inductor; a first bootstrap capacitor coupled between the first end of the inductor and a voltage supply node of the high side driver; a second bootstrap capacitor coupled between the second end of the inductor and a voltage supply node of the low side driver; and a first diode coupled between the voltage supply node of the high side driver and the voltage supply node of the low side driver. The two bootstrap capacitors and are employed on both sides of inductor to provide gate voltage to high side input switch through high side driver in any mode of operation. This allows the regulator to work in all three modes of operation without different external components or configurations depending on the mode.